(Not Applicable)
(Not Applicable)
This invention relates to aircraft antennas and, more particularly, to such antennas providing multiple beam excitation usable with anti-jam adaptive processing to suppress jamming and interference.
A variety of antennas have been made available for reception of Global Positioning System (GPS) signals for navigational and other purposes. A more critical objective than the mere capability to receive such signals, is the objective of enabling reception in the presence of interference or jamming signals. Interference may be the unintended result of reception of signals radiated for some purpose unrelated to GPS operations. Jamming, on the other hand, may involve signals intentionally transmitted for the purpose of obstructing reception of GPS signals. In aircraft operations which are dependent upon use of GPS signals, deleterious effects of interference or jamming may be particularly disruptive.
For reception via a fixed-position antenna in the presence of interference signals incident from a fixed azimuth, for example, a reduced-gain antenna pattern notch aligned to suppress reception at the appropriate azimuth may be employed as an effective solution. However, for aircraft operations a more complex solution is required. With an aircraft and its antenna operable in a variety of geographical locations and conditions, with constantly changing azimuth orientation during flight, interference or jamming signals may be incident from any azimuth and with constantly changing azimuth. At the same time, aircraft maneuvers, such as banked turns, tilt the aircraft and its antenna so that the interference or jamming signals may be incident from different and changing elevation angles.
A variety of adaptive processing techniques have previously been described. Such techniques typically provide an antijam capability based on provision of reduced-gain antenna pattern notches and alignment of such notches at the incident azimuth of undesired incoming signals. However, to enable practical employment of such techniques for aircraft reception of GPS signals, small, reliable, low-cost, low-profile antennas providing a multi-beam capability suitable for anti-jam application are required.
Accordingly, objects of the present invention are to provide new and improved aircraft antennas having one or more of the following characteristics and capabilities:
low-profile configuration of four bent monopoles and four slot elements;
eight elements with eight beam excitation capability;
omnidirectional circularly-polarized principal beam;
seven selectively excitable auxiliary beams;
full upper-hemisphere beam coverage;
multiple elements for omnidirectional and other coverage;
small-size, low-profile implementation;
high-performance, high-reliability design;
excitable in a variety of beam configurations for anti-jam applications; and
controllable pattern excitation suitable for adaptive processing anti-jam operation.
In accordance with the invention, an eight-element anti-jam aircraft antenna includes a cavity assembly, four slot elements and four bent monopole elements. The cavity assembly includes a conductive upper surface spaced above a conductive lower surface. The four slot elements each include a slot in the upper surface configured as a radiating element. The slot elements are arrayed around a vertical axis and extend radially relative to that axis. The four bent monopole elements extend above the upper surface of the cavity assembly and are arrayed around the vertical axis. Each bent monopole element includes an upward-extending first portion and a second portion extending inward toward the vertical axis. The antenna also includes a coupling assembly coupled to the slot elements and bent monopole elements to couple signals for an omnidirectional antenna pattern and a plurality of additional antenna patterns.
The slot elements may be arrayed around the vertical axis at successive angular separations of 90 degrees and the bent monopole elements may be similarly arrayed around that axis.
The coupling assembly of the antenna may be arranged:
(i) to provide 90 degree progressive phase excitation of the bent monopole elements to form a right-hand circularly-polarized omnidirectional antenna pattern;
(ii) to provide 90 degree progressive phase excitation of the bent monopole elements to form a left-hand circularly-polarized omnidirectional antenna pattern;
(iii) to provide same phase excitation of the bent monopole elements to form a uniform phase omnidirectional antenna pattern;
(iv) to provide 180 phase progressive excitation of the bent monopole elements to form a four-lobe antenna pattern; and
(v) to provide four figure-eight type patterns at different azimuth orientations by excitation of the slot elements.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.